Liquid level and composition sensing systems and methods using emf wave propagation

ABSTRACT

An automotive urea solution monitoring device is deployed in conjunction with the urea tank of a selective catalytic reduction vehicle. An RF signal of a constant frequency may be generated across a resonant circuit, which may be comprised of an inductor and a PCB trace capacitor, or the like. Electromagnetic radiation is propagated into the automotive urea solution in the urea tank. The conductivity and dielectric properties of the liquid change the impedance of the discrete/trace capacitor and or the discrete/trace inductor. These changes are proportional to ammonia content, temperature, and/or level of the automotive urea solution in the urea tank and are preferably detected by a microcontroller, or the like, and then transmitted to a selective catalytic reduction vehicle engine management system, or the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No.11/431,912, filed May 10, 2006, entitled System and Method for SensingLiquid Levels Using EMF Wave Propagation; and U.S. Provisional PatentApplication Ser. No. 60/875,439, filed Dec. 18, 2006, entitled FuelComposition Sensing Systems and Methods Using EMF Wave Propagation, bothof which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to systems and methods for sensing thecondition of liquid in a tank or container. More particularly,embodiments of the present invention relate to sensing characteristicsof automotive urea solution in a urea tank in a motor vehicle bypropagating electromagnetic waves into a urea tank.

2. Description of the Prior Art

Selective Catalytic Reduction (SCR) vehicles, also referred to as Euro Vvehicles, are diesel powered motor vehicles which are compatible withthe use of an operating fluid to reduce emissions. Typically, the SCRvehicle has a urea tank, separate from the fuel tank, which is used tocarry an operating fluid such as an automotive urea solution, or thelike. Automotive Urea Solution (AUS) is a solution of high purity ureain de-mineralized water. AUS is stored in a urea tank of an SCR vehicleand is sprayed into the exhaust gases of the vehicle in order to convertoxides of nitrogen into elementary nitrogen and water. An SCR vehiclemay then advantageously satisfy the Euro V Emissions Standard.

It is important for the Engine Management System (EMS) of an SCR vehicleto have information on the composition of the AUS, so that the EMS mayadjust certain vehicle parameters to optimize vehicle performance,specifically emissions control.

In order to ensure this method of reducing emissions in an SCR vehicleremains effective, the quality of the AUS must be maintained.Contaminants, a change in the ratio of high purity urea to otherconstituents, temperature variation or other changes can impact the lifeexpectancy of the AUS and the effectiveness of the AUS at reducingemissions.

SCR vehicles generally rely on the use of direct measurement systems todetermine the level of AUS in a tank. Such systems typically comprise aplurality of sensors disposed at different levels along the verticalplane inside the urea tank. Such sensors typically have poor resolution,are intrusive, and do not detect the quality or temperature of the AUS.Such direct measurement systems also require installation of mechanismsinside the urea tank. Repair, replacement, or adjustment of such aninternal direct measurement system is problematic. Furthermore, suchsystems are ineffective when employed in an SCR vehicle which is exposedto temperatures under minus eleven degrees centigrade, which is thetemperature that AUS typically freezes, because such systems do notprovide a means of measuring AUS temperature to enable the correctapplication of heat to prevent freezing of the AUS.

SCR vehicles generally rely on the use of indirect measurement systemsto determine the effectiveness of the AUS in reducing vehicle emissions.Such indirect measurements are taken from the exhaust fumes and arepassed to the EMS, whereupon the EMS may increase or reduce the quantityof AUS released from the tank. Such systems are typically slow to reactand do not accurately reflect the actual quality or composition of theAUS.

Thus, the prior art fails to provide a reliable, inexpensive, andaccurate system and method of measuring the level or quality of AUS in amotor vehicle urea tank, let alone both.

SUMMARY

The present invention is directed to systems and methods whichaccurately measure the level, temperature and/or quality of liquid,particularly AUS, in a motor vehicle by means of an internal or externalAUS monitoring system. In particular, embodiments of the presentinvention may be used in SCR vehicles to detect certain characteristicsof AUS including the amount of AUS in a urea tank and the percentage ofammonia content, and/or other constituents in the AUS. This informationcan be reported to the EMS or Body Control Module of the SCR vehicle,allowing the EMS to respond accordingly, thereby allowing adjustments tobe made and improve, or at least, maintain the SCR vehicle emissionsreduction performance, quickly and accurately. Embodiments of thepresent invention detect characteristics of the AUS without any directcontact with AUS, minimizing risk of leaks, or wear of the measuringdevice due to exposure to ammonia, or the like. To this end, embodimentsof the present invention may, be deployed in conjunction with the ureatank at the bottom/side of a urea tank or internal to the urea tank.

Embodiments of the present invention may generate an RF signal of avariable frequency across a resonant circuit, which comprises aninductor and a PCB trace capacitor, capacitor plates, and/or the like.Electromagnetic radiation is propagated into the urea tank. Theconductivity and dielectric properties of the AUS change the impedanceof stated trace capacitor/capacitor plates and/or stated inductor. Thesechanges are proportional to certain characteristics of the AUS includingits level and/or the ammonia content of the AUS, and are preferablydetected by a microcontroller, or the like, and then transmitted to theEMS. As such the present systems and methods provide a cost effectivesolution, well suited, not only for original equipment applications butalso for up-fit or retro-fit. The present systems and methods are highlyresponsive and provide immediate information to the EMS, allowingadjustments to be made and improve/maintain the SCR vehicle emissionsreduction performance, quickly and accurately. In various embodiments,auto-compensation may be provided so that the measured electricalparameter provides an accurate indication of the liquid level andcomposition in the tank, independent of variations in operatingconditions, such as ambient temperature. The system can include aphysical or wireless data interface to facilitate external transmissionof the AUS measurement from the system to a central controller in thevehicle. The data can be transmitted periodically, in response to achange, by request from the central controller, or by request from anexternal device such as a diagnostic device.

Thus, in accordance with the present invention an embodiment of a methodfor liquid level and composition sensing using EMF wave propagationmight include generating an RF signal at an operating frequency,coupling the RF signal to a resonant circuit, the resonant circuithaving a resonant frequency and including an inductor positionedproximate to liquid in a tank and measuring a change in an electricalparameter associated with the resonant circuit caused by a variation inat least one property of the liquid proximate to the inductor. As noted,the liquid may be urea. The RF signal may be substantially sinusoidaland may have a constant frequency. The resonant circuit may be aseries-resonant inductor, capacitor, resistor circuit or aparallel-resonant inductor, capacitor, resistor circuit. Preferably theinductor of the resonant circuit in placed in close proximity to thetank, causing electromagnetic radiation to propagate into a spacedefined within the tank, whereby the liquid in the tank acts as anelectrical load to the series resonant circuit in a manner proportionateto the constituents of the liquid in the tank. The property of theliquid may be an electrical property and the measured change in theelectrical parameter may be a function of a variation in the electricalproperty of the liquid. Where the liquid is an automotive urea solution,the variation in the property may be a function of liquid compositionsuch as the ammonia concentration in the automotive urea solution or afunction of the level of the automotive urea solution in the tank. Theaforementioned measuring of a change in an electrical parameterassociated with the resonant circuit may comprise measuring a change involtage at the resonant circuit or a change in the resonant frequency ofthe resonant circuit. Preferably, the operating frequency of the RFsignal may be calibrated to compensate for physical and/or electricalproperties of the tank and such calibration may be carried outautomatically. In particular, calibration of the operating frequency mayinclude sweeping between a range of frequencies, from a first frequencyto a second frequency, to identify the operating signal within the rangeand measuring a parameter of a resonant circuit from the operatingfrequency. The measured parameters may include the resonant frequency ofthe resonant circuit and/or the amplitude of the resonant frequency ofthe resonant circuit. Also, in accordance with the present invention themeasured change I the liquid may be converted to a value representing aconcentration of ammonia in the liquid and the measured change in theliquid may be transmitted to an external device

Embodiments of a monitoring device of the present invention may includean antenna driver having output terminals, and input terminals, coupledto an RF generator; a resonant circuit coupled to the antenna driver andhaving an inductor positioned proximate a liquid in a container or tank;and a controller, including the RF generator, and controlling anoperating frequency of the RF generator to be proximate to a resonantfrequency of the resonant circuit and measuring a change in anelectrical parameter associated with the resonant circuit caused bychanges in the liquid in the tank. Again, the liquid may be anautomotive urea solution and the changes in the liquid may include achange in level of the urea in the tank or a change in concentration ofthe urea, such as a change in ammonia concentration of the urea. Thecontroller, antenna driver, and resonant circuit are mounted on aprinted circuit board, which may be flexible and the sensor may beinstalled external to the container or tank. As noted, the resonantcircuit includes a capacitor, which may be a printed circuit board tracecapacitor.

An embodiment of a system for liquid level and composition sensing usingEMF wave propagation might include an RF generator functional togenerate an RF signal at an operating frequency; an antenna circuitelectrically coupled to the RF generator, the antenna circuit comprisinga resonant circuit and a radiating component mounted proximate to a ureatank, the resonant circuit having a resonant frequency; and a controlleroperatively connected to the RF generator and to the antenna circuit,the controller being functional to sweep between a range of afrequencies, from a first frequency to a second frequency, to identify asignal at the resonant frequency within the range and measuring a changein an electrical parameter of the signal associated with the resonantcircuit caused by changes in a concentration of ammonia in urea in thetank. The controller may also transmit the measured change in theelectrical parameter and/or the controller may convert the measuredchange in the electrical parameter to an ammonia concentration signal.Thus the controller may transmit the ammonia concentration signal to anengine management system of a selective catalytic reduction vehicle. Asnoted, the resonant circuit may be a series resonant circuit. In whichcase the controller may comprise a calibration module operative to sweepbetween a range of a frequencies, from a first frequency to a secondfrequency, to identify a signal at the resonant frequency within therange and measuring a change in an electrical parameter of the signalassociated with the resonant circuit caused by changes in concentrationof ammonia the urea in the tank. The controller might also include acompensation module functional to adjust the ammonia concentrationsignal for changes in ambient temperature or changes in temperature ofthe liquid in the tank.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the systems and methods that follow may be betterunderstood. Additional features and advantages of the systems andmethods will be described hereinafter which form the subject of theclaims of the invention. It should be appreciated by those skilled inthe art that the conception and specific embodiment disclosed may bereadily utilized as a basis for modifying or designing other structuresfor carrying out the same purposes of the present invention. It shouldalso be realized by those skilled in the art that such equivalentconstructions do not depart from the spirit and scope of the inventionas set forth in the appended claims. The novel features which arebelieved to be characteristic of the invention, both as to itsorganization and method of operation, together with further objects andadvantages will be better understood from the following description whenconsidered in connection with the accompanying figures. It is to beexpressly understood, however, that each of the figures is provided forthe purpose of illustration and description only and is not intended asa definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form part ofthe specification in which like numerals designate like parts,illustrate embodiments of the present invention and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 is a perspective view of an external embodiment of an AUS systemof the present invention deployed in conjunction with a urea tank;

FIG. 2 is a partially fragmented perspective view of an internalembodiment of an AUS system of the present invention deployed inconjunction with a urea tank;

FIG. 3 is an exploded perspective view of the AUS monitoring device ofFIG. 1;

FIG. 4 is a block diagram view of certain functional elements within theAUS monitoring device of FIGS. 1, 2 and 3.

DETAILED DESCRIPTION

The present systems and methods can determine the type of liquid in acontainer, particularly where the liquid is substantially water and isnot limited to the examples used in this description. In the illustratedand described embodiments, the present system can provide thisinformation to an automotive EMS, which may use the information toprevent improper operation of SCR vehicles with water or the like in theurea tank rather than the AUS recommended by the vehicle manufacturer,as well as to detect the level and or concentration of urea in a tank.

FIG. 1 shows an embodiment of AUS monitoring device 100 of the presentinvention disposed in conjunction with urea tank 102, such as mountingthe AUS monitoring device to the exterior of the tank. Variousembodiments call for mounting the AUS monitoring device of the presentinvention to the exterior side or bottom of a tank. Urea tank 102 may bemade from a non-conductive material such as plastic. AUS from urea tank102 may be pumped by means of a pump 103 into exhaust 104 of a vehiclefor emission control purposes.

FIG. 2 shows another embodiment (200) of the AUS monitoring device ofthe present invention disposed in conjunction with urea tank 102, suchas mounting the AUS monitoring device 200 to the interior of the tank.This embodiment may be of particular use where urea tank 102 iscomprised of a conductive material, such as metal.

FIG. 3 illustrates an embodiment of AUS monitoring device 100 or 200including PCB 301 disposed in housing 302, shown as having two parts 302a and 302 b. As discussed in greater detail with respect to FIG. 4below, PCB 301 may mount and or define controller 401, the controllermight include RF generator 402 and analog-to-digital converter 403(ADC). PCB 301 might also include antenna circuitry 405 includingantenna driver 406 having output terminals, and input terminals, coupledto the RF generator and resonant circuit 410. Resonant circuit 410preferably includes inductor 411 and capacitor or PCB trace capacitor412 positioned proximate a liquid in tank or container 102.

Embodiments of AUS monitoring devices 100 and 200 illustrated in FIGS.1-3 may employ circuitry similar to circuitry 400 depicted in FIG. 4.Resonant circuit 410, which may be an LCR (inductor-capacitor-resistor)circuit, may be a series or parallel resonant circuit. Resonant circuit410 preferably comprises resistor 413 as well as capacitor 421 andinductor 411 discussed above. Inductor 411 and/or capacitor 412 may bein discrete form, in PCB trace form, or otherwise formed. By placinginductor 411 of resonant circuit 410 in close proximity to tank 102,electromagnetic radiation may be propagated into liquid space 103defined within tank 102. Whereby, the AUS, other liquid, and/or solidsinside the tank acts as an electrical load on resonant circuit 410 in amanner proportionate to the level and/or the constituents of the liquidor the presence of solids in the tank. The conductivity and dielectricproperties of the liquid change the impedance of discrete/tracecapacitor 412 or discrete/trace inductor 411.

The present invention measures properties of a liquid, such as AUS.These properties are preferably electrical properties and a measuredchange in an electrical parameter of the liquid is a function of avariation in the electrical property of the liquid. Where the liquid isAUS, the variation in electrical property may be a function of theamount of the liquid present and the composition of the liquid.Measurements of electrical properties may include measuring a change involtage at resonant circuit 410 and/or measuring a change in theresonant frequency of the resonant circuit, such as may be accomplishedby analog to digital converter (ADC) 403.

Preferably, RF generator 402 generates an RF signal at an operatingfrequency and antenna circuit 405 is electrically coupled to RFgenerator 402. Also, resonant circuit 410 preferably has a frequencyresponse curve centered around a resonant frequency. Controller 401 maybe operatively connected to RF generator 402 and to antenna circuit 410and may be functional to cause the operating frequency of RF generator402 to be proximate to the resonant frequency of resonant circuit 410,and to measure a change in an electrical parameter associated with theresonant circuit caused by changes in the amount of AUS and/or theconcentration and/or the ratio of ammonia in the AUS in tank 102 toother substances.

More particularly, in embodiments of the present systems and methods, asubstantially sinusoidal RF signal of variable frequency is generatedand coupled, employing antenna driver 406, to resonant circuit 410.Consequently, the liquid AUS inside tank 102 or 202 acts as anelectrical load to resonant circuit 410 in a manner proportionate to theAUS level in urea tank 102 and/or certain characteristics of the AUSincluding the constituents and temperature of the AUS in urea tank 102.The loading effect of the AUS on resonant circuit 410 can cause a shiftin the resonant frequency of the circuit, and/or a change in theamplitude of the signal from the circuit, and/or a change in the Q(quality factor) of the resonant circuit. In accordance with variousembodiments of the present invention, the loading effect of the AUS isdetermined by monitoring a change in one or more electrical parametersassociated with excited resonant circuit 410. For example, the voltageacross resistor 413 in resonant circuit 410 may be monitored. Changes inthis voltage may be detected and analyzed by controller 401 (processor415), the EMS, or other circuitry associated with the SCR system, theresults may be used to output a signal indicative of AUS composition,level or temperature. This output can be in the form of a digital oranalog electrical signal.

Controller 401 or similar circuitry of AUS monitoring device 100 or 200is preferably functional to transmit a measured change in an electricalparameter. In particular, controller 401 may be further functional toconvert the measured change in the electrical parameter to an ammoniaconcentration and/or liquid level signal and to transmit this signal, orother information to an SCR vehicle EMS, or the like. The signal, and/orother information may be transmitted via a physical or wireless datainterface to a central controller in the vehicle periodically, inresponse to a change, by request from controller 401, or by request froman external device such as a diagnostic device.

Preferably, the present invention allows for calibrating the operatingfrequency of the RF signal to compensate for physical and/or electricalproperties of respective tank or container and external effects such astemperature. This calibration may be carried out by processor 415 orother circuitry when the tank is empty or full, or otherwise. Forexample, the calibration may be carried out automatically and/orperiodically. The present systems and methods may employ calibrationhardware and software that enable detection of a resonant frequency ofresonant circuit 410 and the amplitude of that resonant frequency signalwhen the tank is empty. Alternatively or additionally, the presentsystems and methods may employ auto-calibration hardware and softwarethat enable detection of the resonant frequency of resonant circuit 410and the amplitude of the resonant frequency signal relative topreviously known values. In particular embodiments, calibration mightinclude sweeping to identify a resonant frequency signal in a rangebetween a first frequency and a second frequency and measuring aparameter of the resonant circuit as the frequency of the RF signal isswept.

Various embodiments of the present invention detect the temperature ofthe AUS. In accordance with such embodiments the AUS monitoring devicemay include other sensors 420 for temperature or humidity, or othersensors. Controller 401 might also include compensation module 421functional to adjust the liquid concentration signal for changes intemperature of the liquid, ambient temperature, and/or other measured orcalculated parameters.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification: Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention. Forexample, as noted, the present systems and methods can sense and measurethe composition of liquid in other containers and/or transmission linesand are not limited to the examples used in this description. The systemcan be used in a wide variety of scientific, consumer, industrial, andmedical environments. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1-35. (canceled)
 36. A monitoring device comprising: an antenna driverhaving output terminals, and input terminals, coupled to an RFgenerator; a resonant circuit coupled to the antenna driver and havingan inductor positioned proximate a liquid in a container or tank; and acontroller, the controller including the RF generator, the controllercontrolling an operating frequency of the RF generator to be proximateto a resonant frequency of the resonant circuit and measuring a changein an electrical parameter associated with the resonant circuit causedby changes in said liquid in said tank.
 37. The device of claim 36,wherein said liquid is an automotive urea solution.
 38. The device ofclaim 37 wherein said changes in said liquid comprises a change in levelof said urea in said tank.
 39. The device of claim 37 wherein saidchanges in said liquid comprises a change in concentration of said urea.40. The device of claim 37 wherein said changes in said liquid comprisesa change in ammonia concentration of said urea.
 41. The device of claim36, wherein the controller, antenna driver, and resonant circuit aremounted on a printed circuit board.
 42. The device of claim 36, whereinthe sensor is installed external to the container or tank.
 43. Thedevice of claim 36, wherein the resonant circuit includes a capacitor.44. The device of claim 43, wherein said capacitor is a printed circuitboard trace capacitor.
 45. The device of claim 41, wherein said printedcircuit board is a flexible printed circuit board.
 46. A systemcomprising: an RF generator functional to generate an RF signal at anoperating frequency; an antenna circuit electrically coupled to the RFgenerator, the antenna circuit comprising a resonant circuit and aradiating component mounted proximate to a urea tank, the resonantcircuit having a resonant frequency; and a controller operativelyconnected to the RF generator and to the antenna circuit, the controllerbeing functional to sweep between a range of a frequencies, from a firstfrequency to a second frequency, to identify a signal at said resonantfrequency within said range and measuring a change in an electricalparameter of said signal associated with the resonant circuit caused bychanges in a concentration of ammonia in urea in said tank.
 47. Thesystem of claim 46 wherein the controller is further functional totransmit the measured change in the electrical parameter.
 48. The systemof claim 46 wherein the controller is further functional to convert themeasured change in the electrical parameter to an ammonia concentrationsignal and to transmit the ammonia concentration signal to an enginemanagement system of a selective catalytic reduction vehicle.
 49. Thesystem of claim 46, wherein the resonant circuit is a series resonantcircuit, and the controller further comprises a calibration moduleoperative to sweep between a range of a frequencies, from a firstfrequency to a second frequency, to identify a signal at said resonantfrequency within said range and measuring a change in an electricalparameter of said signal associated with the resonant circuit caused bychanges in concentration of ammonia said urea in said tank.
 50. Thesystem of claim 46, wherein the controller further comprises acompensation module functional to adjust the ammonia concentrationsignal for changes in ambient temperature.
 51. The system of claim 46,wherein the controller further comprises a compensation modulefunctional to adjust the ammonia concentration signal for changes intemperature of the liquid in the tank.